Autism spectrum disorders (ASD) are common neurodevelopmental syndromes affecting 1% of U.S. children. Comorbid anxiety disorders affect 40 to 50% of children with ASD, causing substantial distress and impairment over and above that caused by ASD alone. High anxiety is associated with increased severity of ASD symptoms and social maladjustment in affected youth. Further, parents of children with ASD consider anxiety- related problems to be among the top two challenges facing their children. [Although standard practice cognitive-behavioral therapy (CBT) has been established as an efficacious and safe treatment for anxiety disorders among typically developing youth, its utility in comorbid cases with ASD remains unknown. To date, no studies have experimentally compared standard practice CBT to a cognitive-behavioral intervention that has been personalized for children with a comorbid presentation of anxiety and ASD.] This gap in the literature is of particular concern because there are no empirically-supported treatment options for youth with ASD and comorbid anxiety, and existing pharmacological interventions may have some disadvantages (e.g., limited efficacy in this population, side effects, and potential for drug x drug interactions). [Accordingly, we are proposing a randomized controlled trial to be conducted at three treatment sites to evaluate the efficacy of personalized CBT for anxiety in ASD (Behavioral Intervention for Anxiety in Children with Autism: BIACA) relative to standard practice CBT for anxiety (Coping Cat program). Over the last five years, the proposed BIACA intervention has been adapted and tailored to the characteristics and needs of high-functioning children with ASD; the Coping Cat program reflects the community standard that has been empirically supported in multiple NIH-funded trials.] In response to the NIH Roadmap Initiative, BIACA employs a modular treatment approach, allowing the intervention to be personalized to each youngster's unique needs. [Thus, the proposed research will: (1) examine the efficacy of BIACA relative to Coping Cat, which represents standard practice treatment, (2) evaluate the maintenance of treatment gains, (3) examine the impact of personalized intervention on functional outcomes such as social responsiveness, loneliness, and friendship quality, (4) test autism severity as a moderator of treatment outcome, and (5) explore other moderators and mediators of treatment outcome.] A total of 180 youth (ages 8-13 years) with ASD and co-occurring anxiety will be randomly assigned to one of the two treatment conditions. The three recruitment sites for this study are UCLA, the University of South Florida (USF), and Temple University. USF will provide data management services. Considering the rising number of children diagnosed with ASD together with the frequency and severity of comorbid anxiety, the proposed work is tailored to the unique needs of youth with ASD and will provide a timely contribution to public health efforts.